The final volume is called The Twice Lost, and it will be out in July 2013.
It's very long and epic, so long that it really could have been two books instead of one, but so packed with plot that I don't see any way it could have been shorter.
And now it's like I'm sitting on a beach after some enormous sweeping wave has just receded out to sea, trying to make sense of the reconfigured landscape and of all the strange detritus around me on the shore. I'm drained and disoriented and very tired. After spending three years immersed in this story, close to these characters, it's hard to say goodbye.
I do have other projects to work on, other goals for the coming year: a half-completed novel for adults to finish, an idea for a new YA. But I can't think about them yet. My mind is still swarming with fragments of the book I've just finished, snatches of dialogue, the light on the water where the mermaids swam away.